BELLRINGER: 10-31-10

Draw the following box and fill in the squares, THIRD box on the last bell-ringer page:

REPLICATION TRANSCRIPTION

Where in the cell does this take place? Where in the cell does this take place?

What is created in this process? What is created in this process?

When does this take place? WHY does this take place?

THE THREE TYPES OF RNA

• There are three types of RNA that help build proteins.

# 1 Messenger RNA (mRNA) brings instructions from DNA in the nucleus to the cytoplasm.

Then mRNA binds to ribosomes.

# 2 Transfer RNA (tRNA) is the supplier.

Transfer RNA delivers amino acids (the building blocks of proteins) to the ribosome to be assembled

into a protein.

Amino Acid

How it binds with mRNA

# 3 Ribosomes are made of Ribosomal RNA (rRNA).

rRNA uses the instructions from mRNA and the supplies from tRNA to assemble the amino acids in

the correct order.

• mRNA brings the instructions.

• tRNA supplies the amino acid parts.

• rRNA builds the proteins using the instructions and amino acids.

RIBOSOME

THE PROCESS OF TRANSLATION

During Transcription, mRNA is made.

The copy of instructions for making proteins on an mRNA strand is in the form of a code.

• Every three letters on a mRNA strand, called a codon, is a

code for a specific amino acid (a building block to make

protein)

The Genetic Code

There are thirty different kinds of amino acids.

Different types of proteins are made with amino acids in different sequences

• The codons on a mRNA strand need to be converted into amino acids.

mRNA codons

Amino Acids

• The process of converting the codons on mRNA into a sequence of amino acids to make a protein is known

as translation.

Each codon codes for a specific amino acid.

CODON CHART

Every three letters on an mRNA strand is a codon.

• Sometimes there are several codons that code for the same amino acid….for instance,

What two codons code for the amino acid “Arg” (Arginine)?

The Genetic Code

T A C C C G T A T T C G A A G G C T

Below is a DNA strand….

During Transcription, what mRNA strand would be made from this DNA?

A U G G G C A U A A G C U U C C G A

Using this mRNA strand, translate the codons into amino acids using your codon chart.

Methionine Glycine Isoleucine Serine Phenylalanine Arginine

THIS IS WHAT TRANSLATION

LOOKS LIKE

Why does mRNA have to be made?

(Why can’t DNA deliver it’s own instructions)

Nucleus

• Translation takes place at the ribosomes (rRNA) of a cell.

Where does mRNA take the instructions so that proteins can be made?

• mRNA brings the codons (message) from DNA to the ribosome (rRNA)

Translation from mRNA to Protein

RIBOSOME

mRNA

Coming from Nucleus

• As translation begins, one end of mRNA strand attaches to a ribosome.

mRNA strand

Ribosome

Step 1

• tRNAs bring amino acids to the ribosomes.

Translation from mRNA to Protein

RIBOSOME

mRNA

Coming from Nucleus

• Each tRNA only carries one amino

acid.

Amino acid

• There are also three nucleotides on the bottom of the tRNA called an anti-codon.

• Anti-codons complementary base pair with the codons on mRNA.

(this is to make sure they are bringing the correct amino acid- If the anti-codon doesn’t base pair with the codon, then the

wrong amino acid was brought)

Anti-codon

• AUG is usually the first codon on the mRNA strand.

• This signals the ribosome to START making a protein.

• A tRNA with anticodon UAC comes and binds with this codon and drops off it’s amino acid “Methionine”.

Methionine

• After the first tRNA binds with its codon, the mRNA slides down so that the ribosome can read

the next codon.

• A new tRNA molecule carrying an amino acid pairs with the second mRNA codon.

Alanine

• The amino acids then bond together.

• Once the first tRNA lets go of it’s amino acid, it is released from the ribosome.

AlanineMethionine

bond

• A chain of amino acids is formed until the stop codon is reached on the mRNA strand.

Stop codon

The end result is a protein